The evolutionary causes of contrasting patterns of pathogen diversity in different host clades are poorly understood. This study tested the hypothesis that older host lineages have fewer pathogens than younger lineages by examining the incidence of fungal pathogens in fern families differing in their time of origin over a span of 300 million years. Fern-fungal records were obtained from the United States Department of Agriculture database, and study effort was estimated by the number of citations to each fern species in the Web of Science. Pathogen discovery rate (PDR) within a fern family was measured as the rate at which pathogens were recorded in relation to the number of citations to species within that family. PDR for fungi in the Basidiomycota and Ascomycota showed significant differences among fern families and significant phylogenetic signal in the Basidiomycota. PDR for Basidiomycota was significantly negatively correlated with clade age of the fern family. Generic and species diversity within families affected PDR positively, although the effects of clade age were still significant. Within the Basidiomycota the effects of clade age were largely accounted for by the rust fungi (Pucciniales) which formed the majority of recorded basidiomycete pathogens on ferns. The most parsimonious explanation was that the rust fungi host-shifted onto fern families in the early to mid-Cretaceous, but have rarely moved onto more distantly related and older families. However, several other hypotheses could not be excluded, including loss of specialized pathogens in older clades as a result of resistance evolution.

Fern gametophytes are an often-overlooked part of field studies on ferns due to the challenge of finding material and the difficulty of identifying wild-collected plants. Most existing gametophyte descriptions are derived from lab-reared plants and while it is thought that many of the morphological features are similar under both conditions, we still have a poor understanding of in situ morphology for most taxa. The goal of this work was to document a set of morphological observations from the gametophytes of six different species collected in situ. We discovered identifiable gametophyte populations of Elaphoglossum latifolium, Hymenophyllum myriocarpoum, Lomariopsis maxonii, Polypodium dulce, Polytaenium cajenense, and Sticherus bifidus during the 2022 OTS Tropical Ferns and Lycophytes course in Costa Rica. Gametophytes were collected in the field, observed, and photographed using stereo and compound microscopy. This work represents the first detailed description for these species' gametophytes from field collections and offers insights into their natural morphology.

Relationships among the major subclades in the fern family Pteridaceae have proven difficult to resolve. Here, we examine the backbone of this large and heterogeneous lineage using both phylotranscriptomic methods and a more focused, curated approach. We find that Pteridoideae and Parkerioideae are together sister to the rest of Pteridaceae and that Cryptogrammoideae is sister to Vittarioideae plus Cheilanthoideae. We find independent support from our phylotranscriptomic analyses, published cytological data, and genomic distributions of substitutions per site for several whole-genome duplication (WGD) events within Pteridaceae, mainly in Vittarioideae and Cheilanthoideae. However, the various inference methods gave differing approximations for the placement of WGD events within each clade. This study demonstrates that phylotranscriptomic analyses, which employ large datasets at the cost of requiring simpler models and potentially a greater risk of systematic error, can be used in concert with more curated approaches to resolve deep phylogenetic relationships. It also provides an example of the difficulty of confidently inferring ancient WGD event placement, even when using multiple methods.

New combinations are made for several ferns in the Hawaiian Islands in the genera Asplenium, Cystopteris, Dicranopteris, and Microlepia: Asplenium dielerectum f. alexandri comb. nov., Cystopteris douglasii var. sandwicensis, stat. and comb. nov., Dicranopteris linearis var. emarginata comb. nov., and Microlepia setosa var. mauiensis comb nov. A new nothogenus, 3Christelliopsis nothogen. nov. is named for hybrids between Christella and Menisciopsis and a new combination, 3Christelliopsis palmeri comb. nov. is made for the hybrid Christella dentata 3 Menisciopsis cyatheoides.